Sewing machines are used for a variety of industrial and manufacturing purposes. In most of these applications the sewing machine is specifically adapted or adjusted to perform a specific repetitive sewing operation. This specific sewing operation will be performed on successive workpieces as rapidly as possible. The efficiency of the machines and the operators, of course, varies directly with the frequency at which properly fabricated workpieces may be produced.
For example, industrial sewing machines fabricate seat covers for automobiles. The seat covers generally are manufactured from layers of fabric material. The top layer may be vinyl, nylon and velour. Other layers are provided for strength and cushioning. In most instances, the layered material is approximately one half inch thick. To improve the appearance of the seat cover, and to reduce friction between layers, a tucked or rolled design often is provided by sewing parallel seams into the seat cover material. Each seam draws the opposite surfaces of the layered material close together, however, the sections of the layered material between seams retain their normal thickness.
The seat cover described above, and many similar products, are manufactured on specially adapted industrial sewing machines. For example, the seat cover could be sewn quite efficiently on a standard chain-stitching sewing machine that is adapted to include a separate needle for each seam to be sewn on the seat cover. Thus, on a seat cover requiring four seams, the sewing machine would be adapted to include four needles. By this arrangement, as the workpiece is passed through the sewing machine, four parallel seams will be sewn simultaneously.
As mentioned above, the machine that is adapted to perform this sewing operation would be the chain stitching type. These machines utilize at least two threads for each needle to establish an interlocking arrangement of threads to firmly hold the upper and lower surfaces of the workpiece in close proximity to one another. This strong interlocking engagement is extremely important in many applications, such as seat covers, since it often is difficult to correct an improperly sewn section after the workpiece has been placed in its final position. Thus, care must be taken during the initial sewing operation to insure that the workpiece is properly stitched, and that no unraveling is likely to occur.
Many stitching arrangements, including chain stitches, are subject to unraveling at the points where the stitching starts and stops. Specifically, at the beginning or end of a chain produced by a chain stitching machine, the threads from which the chain is formed are subject to unraveling. Consequently, precautions must be taken to insure that any unraveling that does occur does not affect the workpiece.
The most common precaution to pretect against unraveling of the chain into the workpiece is to continue production of the stitched chain several inches past the end of the workpiece. Typically, the chain would be extended some five or six inches past the end of the workpiece, and then the machine would be stopped. At this point the extended chains would be severed approximately midway between the needles of the sewing machine and the trailing edge of the workpiece that had just been completed. By this arrangement, two or three inch chains would extend from the trailing edge of the workpiece, and any unraveling that might occur would affect the chain and not the workpiece. It logically follows that the portions of the chains between the severences and the sewing machine needles would provide the necessary protection against unraveling of the chains on the leading edge of the next workpiece. In a subsequent manufacturing step a stitch would be sewn around the perimeter of the workpiece to permanently prohibit unraveling of the chain into the workpiece.
In most sewing operations the severance of the chain stitch between successive workpieces is accomplished manually by the operator of the sewing machine with either standard scissors or an equivalent form of hand held electrical shears. Thus, the worker, who normally sits on the side of the machine into which the workpiece is fed, must stop the machine, pick up the scissors, cut the chains on the opposite side of the sewing machine, place the scissors in a location where they will not interfere with subsequent work, and sew the next workpiece.
The worker generally can complete this chain cutting operation from a sitting position if the sewing machine has only one needle. However, as mentioned above, many sewing machines used for industrial purposes are adapted to accommodate several needles. If, for example, the sewing machine is adapted with four needles, it will be virtually impossible for the worker to remain seated and comfortably reach behind the array of needles to cut all four chains. Thus, the worker using a multi-needle sewing machine must do a substantial amount of reaching and stretching to cut the chains depending from the workpiece. In most instances, in fact, the worker must stand up to have proper access to the chains. It follows logically that the chain cutting task becomes increasingly more arduous as the number of needles on the sewing machine increases. As a result, attempts to increase efficiency by sewing many chains at once results in decreased efficiency on the part of the worker who must cut the chains.
The manual cutting of thread chains is undesirable for at least four reasons. First, a substantial amount of time is required for the worker to stop the machine, pick up the scissors, reach behind the machine, cut the chains, return the scissors to a proper location and start sewing again. The time devoted to this thread cutting task has a substantial effect on the efficiency of the entire sewing operation. Second, the reaching, stretching and frequent standing required to perform the chain cutting operation takes a significant toll on the sewing machine operators. Specifically, employers report a high degree of arm, shoulder and back injuries among sewing machine operators partially as a result of the excess movement required to cut the thread chains. The frequency of these injuries can be better appreciated in view of the fact that a worker typically completes several hundred workpieces in a single day. Third, to manually attain access to the thread chains, the worker must reach into an area which has many moving parts and which is partially out of view. This of course creates a risk of injuries to hands and fingers. Finally, the arrangement of most sewing machines requires the worker to cut the chain left handed, thus making this awkward task even more cumbersome.
Many attempts have been made to facilitate the chain cutting task. For example, some employers have assigned one employee to cut the chains for several sewing machines. This approach, however, adds significantly to operating costs. It also is difficult to schedule the rate of sewing to insure that no machine sits idle while waiting for the thread cutter.
Other attempts have been made to locate sewing machines such that each sewing machine operator can cut threads on an adjacent machine. However, as above, it is difficult to schedule the sewing rate for adjacent machines. Thus, one machine may sit idle waiting for the worker on an adjacent machine to reach a stopping point. Alternatively, one worker could have to stop in the middle of a workpiece to cut threads on an adjacent machine. Either approach results in decreased operating efficiency.
Several attempts have been made to mechanize the cutting of thread chains. For example, a large blade extending perpendicular to the chains has been mounted on the side of the sewing machine toward which the workpiece moves. The blade can be activated to move downward, and thereby cut the chains. This large blade, however, was found to be extremely hazardous in proximity to the parts of the machine where workers might reasonably place their hands. Consequently, this type of cutter generally is placed several feet from the machine to insure the safety of the sewing machine operators. This approach, however, requires an extended table for sewing operations, plus at least one additional set of mechanical pullers to move the workpiece from the sewing machine to the cutter. This arrangement also requires substantially more space than is typically allocated to sewing machines. As a result, there are substantial excess operating costs due to the inefficient use of space. Additionally, the reliance on several mechanical pullers increases the probability of a failure of mechanical parts.
There have been other similar attempts to utilize electrically generated heat to burn through the thread chain. These devices, however, were considered to be fire hazards, particularly in the dusty environment in which the sewing machines often are used.
Accordingly, it is an object of the subject invention to provide an apparatus for trimming the thread chains that are generated in performing a sewing operation.
It is a further object of the subject invention to provide an apparatus that can be safely used to trim the thread chains generated by a sewing machine.
It is an additional object of the subject invention to provide an apparatus that can perform a thread trimming operation quickly, and without interfering with the normal operation of the sewing machine.
It is still another objective of the subject invention to provide a thread cutting apparatus that can be operated in conjunction with existing sewing machines.
It is still a further object of the subject invention to provide a thread trimming apparatus that will not increase the floor space allocated to sewing machines.
It is yet another object of the subject invention to provide a thread cutting apparatus that readily can be adapted to sewing machines having a plurality of needles spaced at varying distances from one another.